As differential devices for vehicles, there are widely employed differential devices with a limited-slip differential mechanism configured to, even when one wheel on the vehicle is lifted and run idle, transfer sufficient torque to the other wheel via a clutch means to prevent situations in which, when the one wheel rises up over ice, snow, or mud, for example, and runs idle, sufficient torque is not transferred to the other wheel to disable the vehicle to be started, or in which the vehicle fishtails during cornering or at sudden starting or the like.
A differential device with a limited-slip differential mechanism includes a clutch means that can limit a differential in a differential means, disc springs that apply pre-pressures to the clutch means, and a differential limiting operation means that presses and operates the clutch means in an axial direction.
In general, the disc springs are arranged in annular storage grooves formed in a differential case opposed to clutch plates, and are configured to be fully compressed into an almost completely flat shape in a differential-limited condition so that the disc springs receive pressure acting on the clutch plates (for example, refer to Patent Document 1).
However, when being fully compressed, the disc springs become warped toward the opposite sides or undergo wear and tear, which causes a problem that no stable initial torque can be obtained. In addition, the fully-compressed disc springs do not allow their spring force to act on the clutch means. Thus, if the disc springs are fully compressed when the clutch means is pressed and operated by the differential-limiting operation means to limit a differential, the spring force of the disc springs does not act on the clutch means, which causes slippage in the clutch means and gives a driver a feeling of strangeness.
To solve such problems, there has been suggested a differential device with a limited-slip differential mechanism in which the depth of storage grooves for storing disc springs are set to be larger than the thickness of the disc springs, thereby preventing full compression of the disc springs (for example, refer to Patent Document 2).